Fix Mission Control label mismapping across fullscreen Spaces

[blsmth]

Summary

• Mission Control's Spaces Bar draws one button per Space including fullscreen ones, numbered by structural left-to-right position. Reconciler.resolve excludes fullscreen Spaces from userIndex, so the two diverge the moment a display has any fullscreen Space, mislabeling every button after it.
• Reconciler already exposes stripIndex (added in Fix fullscreen switching, correct release docs, and enforce the CI lint gate #66 for SwitchPlanner's hop counting) — the 0-based strip position that does count fullscreen tiles, i.e. exactly the coordinate Mission Control's own button numbering uses.
• MissionControlOverlayGeometry.spacesByDisplayAndIndex and MissionControlRowResolution.resolve now key their (display, structural-button-index) → ResolvedSpace lookup by stripIndex instead of userIndex. A structural button landing on a fullscreen tile itself now correctly misses the lookup instead of mislabeling the next nameable Space.
• No live AX capture with a real fullscreen Space open was performed for this pass — see the spec's Deviations section for why that turned out to be unnecessary (the fix reuses stripIndex, an already-shipped, already-tested structural coordinate).

Closes #65

Test plan

• swift build
• swift test (243 tests, 0 failures)
• xcrun swift-format lint -s -r Sources Tests (clean, matches CI's lint gate)
• New regression tests pin the fix against a synthetic [Desktop 1, fullscreen, Desktop 2] fixture in both MissionControlOverlayGeometryTests and MissionControlRowResolutionTests